As stratum corneum cells mature and approach the outer layers of the skin, they undergo many changes. For one thing, the cells become full of keratin protein, which flattens the cells and shuts off most metabolic processes. For another, the total lipid content of the cells decreases, while the quantity of cholesterol in the cells increases.
The foregoing changes in the cells and the exposure of the cells at the skin surface to dry air, result in the dehydration of the cell membranes. Consequently, the cell membranes become crystalline (less fluid) and collapse, resulting in the formation of a layer of skin highly resistant to penetration of water-soluble and lipid soluble materials into the skin. This process is aggravated by natural processes, such as less skin lipid being produced in older individuals.
A number of different saccharides and disaccharides (e.g., sucrose, mannitol and trehalose) or esters thereof have previously been used in cosmetic compositions for moisturizing the skin. While it has been recognized that such products have had a cosmetic moisturizing effect on the skin, there has been no recognition that a specific disaccharide, namely, trehalose enhances penetration of certain beneficial cosmetically therapeutical ingredients into the skin cells.